This invention relates to flextensional transducers and methods for making flextensional transducers. More particularly, this invention relates to specific implementations of flextensional transducers.
In recent years piezoelectric and electrostrictive ceramics have been used in a number of actuator applications. A composite flextensional actuator was developed as discussed in U.S. Pat. No. 4,999,819 to R. E. Newnham et al. in an attempt to meet increase strain (throw).
The development of the xe2x80x9cmooniexe2x80x9d transducer in the late 1980""s for hydrophone applications was discussed in an article by Q.C. Xu et al. entitled xe2x80x9cPiezoelectric Composites with High Sensitivity and High Capacitance for use as High Pressure Sensorsxe2x80x9d published in IEEE Trans. on UFFC, vol. 38, issue 6, pp. 634-639 (1991). The moonie consists of a piezoceramic disk poled in the thickness direction sandwiched between two thick metal end caps. The shallow half moon shape of the machined inner surface of each of the metal end caps provides the xe2x80x9cmooniexe2x80x9d name. When acting as a sensor, the cavity incident axial direction stress is converted into larger radial and tangential stresses of opposite sign, thereby causing d33 and d31 coefficients of the ferroelectric material to add together (rather than subtract) as the effective dh of the device.
To overcome the issue of stress concentration in the region above the bonding layer, these devices were further refined. The end cap transformed into a shape of a musical cymbal; thus this end cap has been called a xe2x80x9ccymbal.xe2x80x9d The cymbal cap is much thinner than a moonie cap, and is easier to manufacture. It operates in a similar fashion to the moonie with the exception that in addition to the displacement due to the flexural motion of the caps, the cymbal has an added contribution from rotational motion.
However, both of these designs share common limitations in force/throw for applications such as isolators, translators, and positioners. The moonie and cymbal end caps are not easily manufactured and require special fabrication tools whenever product dimensions are altered. The issue of bonding is particularly problematic, in that most adhesives do not fare well under cyclic loading, especially if additionally subjected to large temperature excursion. Bonding of flextensionals at room temperature for use in space and cryogenic filter applications is presently untenable.
The recent introduction of the Thunder process developed by NASA has eliminated some of these problems. However, the Thunder process fabricated actuators like conventional flextensional designs require special tooling for each individual size and shape. The Thunder process of manufacture is quite complex as a result of a multilayer CTE differential process using polyimide coatings, oven baking, and precision lapping of the layers.
An electromechanical transduction apparatus is disclosed in U.S. Pat. No. 4,845,688 to Butler. The Butler device includes a polygonal, oval, elliptical or concave actuator housing. Within the actuator housing is an opening with a similar cross-section for housing a flextensional transducer. The Butler device is only able to obtain an amplification factor of about four. When two Butler devices are stacked one on top of another, the bolting between them lowers the efficiency of transforming strain into motion so that there is not twice the movement of one Butler device.
Notwithstanding the usefulness of the above-described devices, a need still exists for a more efficient device for converting strain in one direction into movement (or force) in a second direction. Furthermore, an easier manufacturing method is needed to fabricate these devices.
The invention generally relates to the design, implementation and manufacture of a near-ideal electromechanical amplification apparatus primarily embodied as a flextensional mechanism that may be used for hydraulic, isolation, pump and stretched fiber applications among others. The apparatus of the present invention may be used individually or in tandem, as with the tunable fiber laser, to create mechanical motions. A feature of the invention, is the ability to provide unidirectional free motion axially through the apparatus when driven by piezoelectric, electrostrictive or magnetostrictive means. The concept of the current invention also allows for near ideal amplification or double amplification using a corrugated platten system. The apparatus of the present invention may also integrate the drive electronics within its design using a piezo-microdrive apparatus.
Another feature of the invention is the ability to provide self-contained flextensional mechanisms consisting of the primary embodiment incorporating this transversal embedded electronics driver.